Current internet protocol (IP) technology and mobile IP technology enables a host terminal or host node which is normally connected in a particular network (the nodes ‘home’ network) to temporarily connect into a different network (a ‘foreign’ network) and still receive IP packets or messages sent to the host terminal at its address in the home network. Such a host terminal which changes its point of network attachment is known as a mobile node.
To still receive IP packets in the foreign network the mobile node must register with a so-called ‘home agent’ in its home network. In registering with its home agent, the mobile node provides the home agent with a ‘care-of’ address where it can be addressed in the foreign network. The home agent then monitors traffic in the home network, and if the home agent identifies an IP packet that is carrying a destination address corresponding to the mobile node's home address in the home network, it intercepts the IP packet. The home agent then ‘re-packages’ the IP packet and sends it to the node at the ‘care-of’ address in the foreign network.
The ‘care-of’ address may be a co-located care-of address or a foreign agent care-of address.
The technique of directing an IP packet, destined for an address in the home network, to a ‘care-of’ address in the foreign network is known, in mobile IP, as ‘tunneling’. It is important in tunneling the IP packet to the ‘care-of’ address that certain information concerning the original IP packet is retained in the re-packaged IP packet. For example, as well as maintaining the original payload (or information portion) of the IP packet, the mobile node at the ‘care-of’ address must still be able to identify in, the ‘re-packaged’ IP packet the source address from which the IP packet was originally sent and the home address of the mobile node in the home network.
One technique known in mobile IP for ‘tunneling’ an IP packet to a mobile node ‘care-of’ address encapsulates the original IP packet into a new IP packet as the IP packet payload. That is the original IP packet is incorporated as the payload (or information portion) of the new IP packet without any change to its content. The ‘care-of’ address is added to the new IP packet as the new destination address and the source address of the new IP packet is identified as the home agent. On receipt the mobile node at the ‘care-of’ address removes the ‘wrapping’ on the new IP packet to recover the original IP packet.
This technique suffers from a number of disadvantages. One disadvantage is that the ‘repackaged’ IP packet is longer than the original IP packet. Another disadvantage is that the repackaged IP packet does not facilitate the support of quality of service provisions in conformance with existing IP quality of service standards.
Each IP packet has associated therewith, and included in the IP packet, flow identification information which identifies the quality of service associated with the IP packet transmission. This flow identification information is present in fixed locations of the IP packet, where quality of service (QoS) capable routing/switching elements can locate it and operate in dependence on it. However, with the encapsulation tunneling technique the flow identification information included in the IP packet by the source originating the IP packet is not available between the home agent and the ‘care-of’ address.
Thus the fundamental problem with this encapsulation technique in conventional mobile IP (one of which is known as IP-in-IP encapsulation) is that it shields the real source address (i.e. the address of the correspondent node) and real destination address (i.e. the mobile node's home address), as well as the protocol ID in the IP packets, from the home agent to the mobile node. In addition, encapsulation mobile IP also changes the payload infrastructure (the original IP header becomes part of the payload) and fails flow differentiation if routers are not changed accordingly so as to be able to detect the modifications or changes. Changes or even slight modifications of routers often requires a large amount of re-design and re-placement of all existing routers. This far more complicates the control and management of the networks. It may also cause lots of problems in terms of security control and inter-operability.
It is therefore an object of the present invention to provide a ‘tunneling’ technique which enables the flow identification information included in the original IP packet transmitted by the source to be available throughout the routing of the IP packet to the mobile node's ‘care-of’ address.